This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Numerical Simulations to Study the Role of Biomechanics in Tactile sensation PI: Dr. Mandayam A. Srinivasan, Director, MIT Touch Lab Abstract The biomechanics of skin tissues play a major role in the human tactile mechanisms. When our fingers come in contact with an object, surface loads imposed on the finger pad are transmitted to embedded nerve terminals (mechanoreceptors) in the skin tissues. These mechanoreceptors generate neural codes of the mechanical signals, enabling us to feel the object. Unlike visual and auditory mechanisms, modeling tactile encoding mechanisms has been a challenge and is as yet an unsolved problem. To better understand the mechanics of contact between the skin and an object, it is imperative to have a good understanding of the mechanical properties of the underlying tissues. To gauge the role of skin biomechanics in tactile response, two dimensional (Srinivasan and Dandekar, 1996;Maeno et al, 1998) and three dimensional finite element (FE) models (Dandekar, Raju and Srinivasan, 2003) of the human and monkey fingertips with realistic external geometry and internal layered structure of the skin and subcutaneous tissues have been developed using linear elastic models of the underlying tissue. These models enabled researchers to estimate the stress state at mechanoreceptor locations and relate it to the mechanoreceptor neural response. Dandekar et al. (2003) hypothesized that the strain energy density at a mechanoreceptor location is a good candidate to be the relevant stimulus for SA-I mechanoreceptors. The 3D finite element simulations for this study were conducted using the resources at the NSF Pittsburgh supercomputing Center. The present study is a follow up to the work done by Dandekar et al. (2003) which was based on purely elastic material models. The goal of present study is to develop viscoelastic finite element models (using ADINA) of the primate finger capable of predicting rate dependent mechanoreceptor responses to dynamic loading. In addition to this we will utilize similar methods to study the biomechanics of a new model organism, the nematode, C.elegans. We have recently completed experiments to characterize the viscoelastic properties of primate fingertip and elastic properties of C. elegans tissue through micro and nano mechanical stimulation. In addition, we have data on the surface deflection of primate fingertips to line loads (Srinivasan, 1989). The present work will be focused at developing realistic finite element models for the primate finger and the worm, calibrating these models by simulating the indentation experiments in ADINA and matching the model response with available experimental data (line load surface deflection data (Srinivasan, 1989) as well as force response from our indentation experiments). These calibrated models will then be used to predict biomechanical and neurophysiological response of mechanoreceptors and match with data already present in literature (Srinivasan and Lamotte, 1991 and OHagan et al, 2004). References Dandekar, K., B.I. Raju and M.A. Srinivasan, (2003). "3-D Finite-Element Models of Human and Monkey Fingertips to Investigate the Mechanics of Tactile Sense." Journal of Biomechanical Engineering, Vol. 125, pp. 682-691, ASME Press. Maeno, T., Kobayashi, K., and Yamazaki, N., (1998), Relationship Between the Structure of Human Finger Tissue and the Location of Tactile Receptors, JSME Int. J., 41, pp. 94100. Srinivasan, M.A., (1989). Surface deflection of primate fingertip under line load. Journal of Biomechanics 22, 343349. Srinivasan, M. A. and K. Dandekar (1996). "An investigation of the mechanics of tactile sense using two dimensional models of the primate fingertip." Journal of Biomechanical Engineering 118: 48-55. Srinivasan, M. A. and R. H. LaMotte (1991). Encoding of shape in the responses of cutaneous mechanoreceptors. Information Processing in the Somatosensory System. Wenner-Gren Intl. Symposium Series. O. Franzen and J. Westman, Macmillan Press. O'Hagan R, Chalfie M, Goodman MB, (2005). "The MEC-4 DEG/ENaC channel of Caenorhabditis elegans touch receptor neurons transduces mechanical signals". Nature Neuroscience;8 (1): 43-50